Ballast water is the seawater that is put into a ballast tank of a ship in order for the ship to maintain its balance while sailing without goods.
The increasing volume of internal trade has led to an increase in the ratio of marine transportation, so that the numbers and sizes of the ships also have been increasing rapidly. Thus, the volume of ballast water used in ships has also increased considerably. As the volume of the ballast water used in the ship has increased, the damage done to the endemic marine ecosystem resulting from it being attacked by exotic marine organism species is also increasing. In order to address the international environmental contamination problem, the Internal Maritime Organization (IMO) completed the ‘International treaty concerning control and management of ballast water and sediment of ships’ in 2004, which became effective in 2009.
As a conventional method of treating ballast water, methods of exchanging ballast water while on the sea or land treatment methods were used but are ineffective. Thus, methods whereby a ballast water treatment system is installed in a ship have been widely used. Particularly, the ballast water treatment system mainly uses a filtering method using a filter.
FIG. 1 is a sectional view showing a conventional ballast water filtering apparatus, FIG. 2 is a view showing the process of coupling an upper portion of a housing to a housing body, in the apparatus of FIG. 1, FIG. 3 is a view showing a coupling relation between a core and a driving shaft of FIG. 1, and FIG. 4 is a view showing the process of separating the upper portion of the housing from the apparatus of FIG. 1.
Referring to FIGS. 1 to 4, the conventional ballast water filtering apparatus includes a housing a having an inlet and an outlet which permits the inflow and outflow of the ballast water, a filter b filtering the ballast water which flows in the housing a, a core c serving as a discharge passage for foreign substances fed through a suction nozzle which sucks foreign substances adhering to the filter b, and a driving shaft d driving the core c. The housing a has the inlet and the outlet, and is divided into a housing body a1 that defines a space to accommodate the filter b therein, and a housing cover plate a2 that is coupled to the housing body a1 to seal the housing. Particularly, the housing cover plate a2 is integrally coupled at its upper portion with an exhaust unit e which serves to discharge foreign substances passing through the core c.
Thus, as shown in FIG. 2, when a worker desires to couple the housing cover plate a2 to the housing body a1, first, the core c and the driving shaft d must be coupled to each other. Subsequently, the housing cover plate a2 is coupled to the housing body. If the housing cover plate a2 is first coupled to the housing body, it is impossible to couple the core c with the driving shaft d using the exhaust unit e, so that it is difficult to easily couple the housing cover plate with the housing body. Particularly, the housing cover plate a2 is integrated with the exhaust unit e, so that the weight comes to about 1 ton. Thus, it is more difficult to precisely align and couple the housing cover plate a2 with the driving shaft d, the core c, the filter b and the housing body a1 using a crane. Furthermore, disassembly work is also complicated.
Further, in the conventional filtering apparatus for treating ballast water, as shown in FIG. 3, when it is required to couple the core c with the driving shaft d, the driving shaft d is inserted into a predetermined portion of the core c, and then the driving shaft d and the core c are joined together using the spring pin c1 which passes through the outer circumference of the core c to be inserted therein. The spring pin c1 used in this apparatus is constructed so that it is hollow therein, and is cut at a predetermined portion thereof. Thus, when the spring pin is inserted into the core, the core c and the driving shaft d are firmly coupled to each other by the elasticity of the spring pin. However, the spring pin c1 is hollow therein, so that its strength is weak. Thereby, the spring pin is apt to break or be corroded when there are frequent vertical movements and rotations of the driving shaft d and the core c and the spring pin is used in a marine environment where there is a high salt concentration, so that durability is low.
Further, since the spring pin c1 passes through the outer circumference of the core c to be inserted therein, the length of the spring pin is almost equal to the diameter of the core c. If the elasticity of the spring pin c1 is reduced because of the frequent vertical movements and rotations of the driving shaft d and the core c and vibrations, a portion of the spring pin c1 may be moved out of the core. In this case, when raising the housing cover plate a2 for the future disassembly or replacement as shown in FIG. 4, the housing cover plate a2 may be caught by the portion of the spring pin c1 which is moved out of the core, so that it becomes more difficult to disassemble the housing cover plate a2 using a crane.
Further, if a space (especially, the upper space), such as a ship, in which the ballast water filtering apparatus is installed is not sufficiently large and is limited, it is necessary that the driving shaft d and the core c be previously separated so as to pull the core c and the driving shaft d out of the housing a.